It is known to equip an electronic circuit with a tamper-evident detection part, in particular in order to monitor the authenticity of products with respect to possible counterfeits. This detection part may generally be incorporated into an integrated circuit of CMOS type acting as a transponder. A tamper loop to be placed on a product to be authenticated is linked to terminals or connection pads of the electronic circuit connected to the detection part. The detection part monitors the presence, or lack thereof, of a short circuit between the two connection terminals, that is to say monitors whether the tamper loop is broken or unbroken.
In the case of a product such as a bottle of wine, the tamper loop may be integrated for example into the cork, and may be broken when a corkscrew is introduced. The detection part therefore makes it possible to monitor whether the loop is broken or unbroken. As a result, it is not possible to reuse the electronic circuit, which may be a transponder, in a counterfeit product in such a way as to make people believe that it is an authentic product. It must also be possible to communicate via the transponder before and after the opening of the bottle, that is to say after the destruction of the loop or of the short circuit. The antenna of the transponder is therefore not able to be used as a tamper loop, as this would impede the communication of wireless signals to or from the transponder to an RFID reader.
In the patent application US 2006/0214789 A1 and with reference to FIG. 1, a description is given of an RFID transponder 100 of passive type with a security sensor, such as a tamper loop 101. The transponder comprises at least one antenna 110 in order to be able to communicate with an RFID reader 200 via an antenna 210. The RFID transponder 100 comprises separate terminals for connecting the tamper loop 101. The transponder 100 also comprises a radiofrequency signal reception and transmission unit 102 linked to the antenna 110 and supplying power to a power supply circuit 105. A logic unit 103 is provided with a memory in which an identification code to be transmitted is stored, and which is linked to a circuit 104 for detecting the state of the tamper loop.
In this patent application US 2006/0214789 A1, there is nothing described with regard to using such a tamper loop for a transponder that has to work under various RF electromagnetic fields. There is no provision made to design such a loop for a transponder capable of receiving or of transmitting signals at different carrier frequencies, this constituting a drawback.
In the U.S. Pat. No. 9,082,057 B2 and with reference to FIG. 2, a description is given of an RFID transponder 100 of passive type with a tamper loop 101. The transponder 100 comprises a radiofrequency signal receiver 102 and transmitter 109. It also comprises a non-volatile memory 106 for storing various data, including the state of the tamper loop, and a state detection circuit 107 linked to a unit 108 for managing the loop.
For this tamper loop 101, this requires three connection terminals with one terminal linked to the ground terminal, one terminal linked to the management unit 108 and one terminal linked to a current source Ipol by way of a resistor R1. Another resistor R2 is arranged between the terminal linked to ground and the one linked to the management unit 108. As in the preceding document, there is no provision made to design a tamper loop for a transponder receiving or transmitting signals at different carrier frequencies, this constituting a drawback.
FIG. 3 shows an overview of the principle of operation of a tamper loop 101 connected to two connection terminals Tamper_in and Tamper_out of the integrated circuit of a transponder. A logic input signal Tamper_en controls the use of the unit for managing the state of the tamper loop 101. This input signal Tamper_en makes it possible to control the closure of a first switch S1 linked between a current source I1 linked to a supply voltage Vsup and a first connection terminal Tamper_in of the loop. The input signal Tamper_en also makes it possible to control the closure of a second switch S2 between a second connection terminal Tamper_out of the loop and a current source I2 linked to ground.
The value of the current from the current source I1 is greater than the value of the current from the current source I2, for example 10 times greater. An inverter 120 may also be provided by connection to the second connection terminal Tamper_out for supplying an output signal Short for the state of the tamper loop 101. When the two switches S1 and S2 are closed, the state of the output signal of the inverter 120 is in the low state so as to indicate that the tamper loop is not broken, and in the high state if the loop is broken.
No prior art document describes the use of two different frequency ranges for a communication of data from a transponder that is equipped with a tamper loop. These frequency bands are for example the HF band at 13.56 MHz for NFC near-field communications and the UHF band at 915 MHz for long-distance communications. As the tamper loop may be in any form, it may behave as a radio antenna in a noisy electromagnetic environment. As a result, it is necessary to implement electromagnetic compatibility (EMC) circuitry in order to obtain an appropriate measurement of the state of the tamper loop.
The transponder generally operates at a low power, which power is limited depending on the electromagnetic field used for the communication. Under these conditions, it must be mandatory for the tamper-evident function of the circuit to consume little current while having a measurement time that is short enough to determine the state of the tamper loop. It must also not be disturbed by a parasitic capacitor of an external assembly connected to the terminals of the tamper loop when the latter is absent or broken.